Re: changes to kiobuf support in 2.4.(?)4

[Andrea Arcangeli <andrea@suse.de>]

On Thu, Aug 02, 2001 at 08:23:37AM +0000, Gerd Knorr wrote:
> >  The reason of the large allocation and to put the bh inside the kiobuf
> >  is that if we do a small allocation then we end with a zillion of
> >  allocations of the bh and freeing of the bh at every I/O!! (not even at
> >  every read/write syscall, much more frequently)
> 
> That is true for block device I/O only.  Current bttv versions are using
> kiobufs to lock down user pages for DMA.  But I don't need the bh's to
> transfer the video frames ...

I guess you use map_user_kiobuf to provide zerocopy to read/write too
(not just to user-mapped ram allocated by bttv), right?

If you allocate the kiobuf not in any fast path the vmalloc and big
allocation won't be a real issue even now, however I agree it's ok to
split the bh/block array allocation out of the kiobuf to make it lighter
(but still it won't be a light thing).

Andrea